Electrode surface process in gaseous plasma

Abstract

The effect of dense oxygen plasma on the electrode surface was studied by means of an electron microscope. Copper and aluminum films of several hundred ångströms thick obtained by evaporation under vacuum were used as anode in the Self Sustaining Dipole Discharge (S.S.D.D.). The interesting feature of this new type of discharge is to provide a local intense electric field at the electrode surface which enhances the outward migration of metal ions and, therefore, produces a strong surface corrosion. This phenomenon is similar to the anodic oxidation in the electrolytic cell. The only difference would be that in electrolysis a liquid plasma is created at low applied voltage and high electric current, while in the S.S.D.D. a gaseous plasma is produced at relatively low discharge current and high applied voltage. The electrical breakdown over the newly formed oxide layer is, therefore, dominant in the latter case while the thermal breakdown seems to be more important in the electrolysis case. The thick oxide film formed in the present experiment was torn into fissures by both electrical and thermal breakdowns over the entire surface. At some places matter was even completely evaporated, leaving holes on the metal film. Diffraction patterns of selected areas revealed the existence of δAl 2O 3 with aluminum film and Cu 2O and CuO with copper film. Nucleation and growth of oxide is expected in the depth of the metal as a result of oxygen ion bombardment from the plasma.